Audio frequency transformer



Mar. 5, 1929'. J. A. vlc'roREEN 1,703,912

AAUDIO FREQUEICY TRANSFORIER Filed Feb. 21. 1927 N i w w v4a scale and .consequently Patented Mar. 5, 1929.

UNITED STATES JOHN A. VICTOREEN, F CLEVELAND, OHIO.

AUDIO FREQUENCY TRANSFORMER. I

Application led February 21, 1027. Serial No. 169,809.

This invention relates to transformers and moreA particularly to transformers for coupling vacuum tubes for amplifying frequencies within the audible range.

5 Heretofoie transformers for coupling vacuum tubes in audio frequency amplifiers for use in musical reproduction have notl am lifled efficiently on low frequencies or ow notes; have been unable xt0 respond satisfactorily to frequencies or notes of the order of 50 cycles or less; or have caused distortion to those frequencies or notes which they did amplify; and many such transformers have possessed two or more of these serious disadvantages.

I have discovered, however, that it is possible to construct a transformer whichwill amplify fr uencies or notes in the musical scale and as ow as about 50 cycles with practically no attenuation; which will res ond y satisfactorily to frequencies or notes of om about 50 cycles dow'n to about 16 cycles; which will respond effectively to frequencies of from labout 16 cycles to about I5 cycles; that is, well above 50% of the maximum amplifications at any vfr uency'l andwliich will also cause substantia y no distortion of` the wave form of a current ornote within them limits of the musical scale and its neceary harmonics, that is within the useful musical scale. Since it is well known in the art that frequencies from 16 cycles to 50 cycles are at least as important in giving naturalness and body to music and voice reproduction as the higher frequencies, it will be seen that my improved transformer is greatly superior to the prior art devices.

Many of the priorv art transformers, also possessed resonant points above the useful i 4p musical scale but within audibility and consequently amplified 'static and other disturb-A ances unnecearily. My improved transformer, however, has a marked tendency to suppress frequencies above the useful musical eatly diminishes static and other outside disturbances.

` Prior art transformers,'with which I am familiar, have high amplification constants as compared with the constant of my transformer. Such prior art transformers often set up sustained frequencies orI oscillations within the audible range between theloud speaker and the detector tube, caused by the mechanical vibration of the detector tube,

probably at some resonant point. Special sockets .have been devised to prevent such mechanical vibration. With myl transformer, however, no such sustained frequen-.

lciesare set up due, I believe, to the absence `or tone quality necessarily causedby the detuning of the set.

With my transformer it isossible to control the variation`| of ampli cation or frequencies or notes within the entire musical range and its necessa harmonics to within a few percent, that is to cause these frequencies to be amplified in the desired proportion; and to amplify both the small currents and large currents substantially the same number of times. This is true whether the amplification is considered inV either of two w'ays; first a'sinvle cycle, and second, a series of cycles. In the former case is meant substantial absence of wave form distortion; that is a current input in the primary winding tending to rise and fall at a uniform rate w' l cause the voltage in the secondary winding to rise and fall at the same rate as in the primary. In other words, the transformer will not distort the' signal Wave form in transy ferring it from one tube to the next tube. In the latter case, 'a series of cycles or notes whose amplitudes are weak or small will be amplified in the same proportion as a series of c clos or notes whose amplitude variations are arge. For these reasons, my transformer may be said to. possess substantially linear characteristics. A transformer possessing the foregoing properties may be briefly described' as consisting, in a preferred form, of a coil com risl ing primary and secondary windings of a out a one to one ratio with about 6,000 turn's of Y wire in each, the wire of the primary being of such size as to carry the current necessary for the power tube connected to the primary circuit and the wireof the secondary heilig of about size 40, in combination with a core of iron or other material of high' permeability whose effective cross sectionall area is equivalent to at least about two square inches of standard silicon transformer steel and whose average magnetic pathis about 4 or 5 inches. Certain variations from the foregoing preferred sizes and dimensions'may be made but with correspondingly varying results. For example, the ratio of primary yto secondary may vary between about 2 to 1 and about 1 to 2 butv the distortion increases each way from the one to one ratio. The turn value may -vary from about 3500 to about 8500 with distortion increasing toward each limit, but not beingparticularly marked or objectionable for considerable variations either side of the 6000 turns mentioned. The iron core may vary in cross sectional area from about 111/3 sq. inch to the limit of practicability with slightly improved 'results above 2 square inches. The average magnetic path is kept ous frequencies within the musical scale and"V its necessary harmonics, signal amplitudes are requlred which vary 'inversely as the squares of the frequencies. i "l`herefore, i-t is necessary in amplifyingr the low frequencies, tli'at means be employed to handle the necessarily large amplitudes of such frequencies. My transformer will handle such extra large signal amplitudes substantially without distortion. Because of this capability I'preferably employ a power tube in each stage of audio amplification, they transformer being capable of withstandingY the necessarily large plate current when used as a coupling between two such power tubes. This property of my transformer is'traceable, I believe, notonly to the. specified ratio and turn value butv also partly to the extremely large' primary inductance which`v in the preferred form of the device previously described, should exceed about 250 henries and may exceed 400' beni-ies, both as calculated from the formula, in conjunction with the use of correspondingly increased voltage which should exceed .about 250 volts with tubes capable of han-` dling large signal variations.

By reason of the very large impedance and low resistance of the-primary winding of my` transformer, a loud speaker may be placed directly across the primary winding which will advantageously operate to pass the direct current of the plate circuit of the power tube around the loud speaker, substantially with- Yout effecting the quality or volume of the signal applied to the loud speakerfrom theplate circuit of the power tube, thereby eliminating the usual 2 microfarad condenser in series with the loud speaker.

Moreover, for this same reason complicated switching arrangements need not be use'd between l'stages when it is desired to shift the number of stages of amplification in use as the loud speaker or other indicating device may be directly placed or plugged across the primary winding in any stage without noticeable loss of any kind due to such parallel connection.

In the drawings forminga part of this specification and illustrating one form of apparatus embodying my invention and its characteristics Fig. 1 is a vperspective view of a transfor-m-` iron, which may be built up of laminations 3 f each of which is. formed of two Vparts as shown, or may be formed of any desired number of parts; and a coil 4 of layer wound wire comprising primary and secondary windings.

In Fig. 2 I have indicated by curve 169 the property possessed by my transformer in amplificatingsignal currents at various frequencies, and by curves 168 and 170 the corresponding properties possessed by certain of the better transformers of the prior art which I have tested. .It will be noted that the variations of these latter ltransformers are greater than the vari ations of my transformer and also that those transformers are incapable of responding to frequencies between about 5 andabout 50 cycles. It will be understood that the curves are not extremely accurate vonlthe very low frequencies but these curvesfdo indicate the relative values of the respective transformers.

y In Fig. 3 I haveindicated by curve 174 the property possessed by my transformer of producing an'output in the secondary windings which. varies uniformly witlfthe input in the primary winding. Curves 17 2 and 17 3 show the corresponding properties ossessed by the prior art transformers re erred to above. Since these curves indicate the amount of distortion produced, it willbe seen that my improved transformer is markedly superior, in respect to its quality of reproduction, to these' prior art transformers.

It will be understood that the foregoing 'detailed descrip-tion vhas been given for the purpose of enabling those skilled in theart to practice my invention, andinot for the purpose oflimiting my invention thereto. Va-

y primary,

Visis rions changes may be made'in the apparatus vdescribed in detail within the spirit of my invention, the scope of which is defined in what is claimed:

What is claimed is 1. An improved transformer for coupling vacuum tubes in audio frequency amplifiers comprising primary and secondary windings' winding being between 3500 and 8500 and the area of the core being such as to cause approximately the same variation of output on vthe secondary as the variation in input in the throughout the useful musical y scale.

- 3. An improved .transformer for coupling vacuum tubes in audio frequency amplifiers comprising primary and secondary windings having a ratio of from about 2 to 1 to about 1 to 2, and a turn value of about 6000; and an iron core having such a cross sectional area and effective magnetic length as, in conjunction withl the said windings, will cause notes throughout the useful musical scale to be amplified substantially uniformly and will cause the variation in secondary output to follow closely the variations in primary Vinut. P4. An improved transformer vfor coupling vacuum tubes in audio frequency amplifiers comprising primary and secondary windings having a ratio of approximately 1 to 1 and a turn valueof between about 3500 and 8500;V

and an iron core having such a cross sectional area and effective magnetic length as in conjunction with said windings will cause notes throughout the useful musical scale to be amplified substantially uniformly and will cause the variations in secondary output to follow closely the variations in primary input.

5. An improvedtransformer for coupling vacuum tubes in audio frequency amplifiers comprising primaryj and secondary windings, having a ratio of between about 2 yto 1` and about 1 to 2 and a turn value of between' about 3500 and 8500, and a core, the transformer being capable of amplifying frequencies throughout substantially the entire usecomprising primary and secondary windings having` a ratio-of approximately one one and a turn value of between about 4000 and 7000, and an iron core having a cross-sectional aiea of about two squai'e inches and an effective magnetic length of about four or five inches.

7. An improved transformer for coupling vacuum tubes in audio frequency amplifiers having substantially linear characteristics and comprising primary and secondary windings having a ratio of`approximately one to one and `a turn value of between about 3500 and 8500, and an iron core having a cross sectional area of about two square inches and an effective magnetic length of about four or five inches;

8. An improved transformer for coupling vacuum tubes in audio frequency amplifiers having substantially linear characteristics and Acomprising primary and secondary windings, having a ratio of approximately one to one and a turn value of about 6000,

andfa core having aiieffective magnetic length of four or five inches and composed of magnetic material substantially equivalent to a standard iron core having across sectional area above about one and a half square inches. l

9. An improved transformer for coupling vacuum tubes in audio frequency amplifiers having substantially linear characteristics and comprising primary and secondary windings, having a ratio of approximately one to one and a turn value of between about 4000 and about 7 000, and a core`having an effective magnetic length of about four or five inches and composed of magnetic material substantially equivalent to a standard iron core having a cross sectional area above about one and a half square inches. 10. An improved transformer for coupling vacuum vtubes in audio frequency amplifiers pling vacuum tubes in audio frequency amrplifiers comprising primary and lsecondary windings, having a ratio of from'about two to one to about one to two and a turn value of` about 6000, and a core having an effective magnetic length of about four or fivev inches and composed of magnetic material substantially equivalcnt'to a standard iron vcore having a cross sectional area of about two square inches. i f y y i 12. An improvedv transformer for coupling vacuum tubes in audio frequenc amplifiers having substantially-1 linear c aracthel transformer being capable of amplifying f frequencies throughout substantially the entire useful musical scale and also of amplify* ing without'serious loss of amplification, frequencies as low as about 16 cycles.

13. An improved transformer for coupling vacuum tubes in audio-frequency amplifiers comprising primary and` secondary windings, having a ratio of about one to one, and a turn value of about 6000, and a core of suitable magnetic material and suitable magnetic length and cross sectional area, the transformer being capable of amplifying frequencies throughout .substantially the. entire useful musical scale and also ofamplifying without serious loss of amplification, frequencies as low as about 16 cycles.

14. An improved transformer'for cou pling vacuum tubes in audio frequency amplifiers comprising primary and secondary windings, having a ratio of ybetween about two to one and about one to two and a suitable turn Value, and a corehaving an effective magnetic length of about four or, fire inches and composed of magnetic material equivalent substantially toa standard iron core having a cross sectional area of above about one and a half square inches, the transformer being capable of amplifying frequencies throughout substantially the entire useful musicalscale, and also of amplifying without serious loss of amplification, frequenciesv as low as about 16 cycles.

In testimony whereof I hereunto affix my signature this 18th day of February, 1927.

JOHN A. VICTOREEN. 

